The Holocene or sixth mass extinction

 

The new study that’s generated so much conversation estimates that as many as three-quarters of animal species could be extinct within several human lifetimes, which sounds incredibly alarming.

Scientists analysed both common and rare species and found billions of regional or local populations have been lost. They blame human overpopulation and overconsumption for the crisis and warn that it threatens the survival of human civilisation, with just a short window of time in which to act.

Previous studies have shown species are becoming extinct at a significantly faster rate than for millions of years before, but even so extinctions remain relatively rare giving the impression of a gradual loss of biodiversity. The new work instead takes a broader view, assessing many common species which are losing populations all over the world as their ranges shrink, but remain present elsewhere.

The scientists found that a third of the thousands of species losing populations are not currently considered endangered and that up to 50% of all individual animals have been lost in recent decades. Detailed data is available for land mammals, and almost half of these have lost 80% of their range in the last century.

The scientists found billions of populations of mammals, birds, reptiles and amphibians have been lost all over the planet, leading them to say a sixth mass extinction has already progressed further than was thought.

Each of the previous extinctions wiped out between 50 and 90 percent of all species on the planet.

The most recent occurred about 65 million years ago, when an asteroid ended the reign of the dinosaurs.

The scientists conclude: “The resulting biological annihilation obviously will have serious ecological, economic and social consequences.

Humanity will eventually pay a very high price for the decimation of the only assemblage of life that we know of in the universe.”

They say, while action to halt the decline remains possible, the prospects do not look good: “All signs point to ever more powerful assaults on biodiversity in the next two decades, painting a dismal picture of the future of life, including human life.”

Wildlife is dying out due to habitat destruction, overhunting, toxic pollution, invasion by alien species and climate change. But the ultimate cause of all of these factors is “human overpopulation and continued population growth, and overconsumption, especially by the rich”, say the scientists, who include Prof Paul Ehrlich, at Stanford University in the US, whose 1968 book The Population Bomb is a seminal, if controversial, work.

Earth’s five previous mass extinctions

End-Ordovician, 443 million years ago

A severe ice age led to sea level falling by 100m, wiping out 60-70% of all species which were prominently ocean dwellers at the time. Then soon after the ice melted leaving the oceans starved of oxygen.

Late Devonian, c 360 million years ago

A messy prolonged climate change event, again hitting life in shallow seas very hard, killing 70% of species including almost all corals.

Permian-Triassic, c 250 million years ago

The big one – more than 95% of species perished, including trilobites and giant insects – strongly linked to massive volcanic eruptions in Siberia that caused a savage episode of global warming.

Triassic-Jurassic, c 200 million years ago

Three-quarters of species were lost, again most likely due to another huge outburst of volcanism. It left the Earth clear for dinosaurs to flourish.

Cretaceous-Tertiary, 65 million years ago

An giant asteroid impact on Mexico, just after large volcanic eruptions in what is now India, saw the end of the dinosaurs and ammonites. Mammals, and eventually humans, took advantage.

The 6th extinction is man made

Previous extinctions were often linked to asteroids or volcanoes, but this one is man made.

Species are disappearing up to 114 times more quickly than they did during previous mass extinctions.

Extinction is a natural part of evolution, having already claimed an estimated 99 percent of all species in Earth’s history,  but when too many species die out too quickly, it creates a domino effect which is capable of bringing down entire ecosystems.

Loss of habitat

The main cause of wildlife declines is loss of habitat and fragmentation which is the primary threat for 85 percent of all species on the IUCN Red List. That includes deforestation for farming, logging and settlement, but also the less obvious threat of fragmentation by roads and other infrastructure.

Invasive species

Invasive species now threaten a variety of native plants and animals around the world, either by killing them directly or by beating them to food and nest sites.

Pollution

Pollution is pervasive on land, in the air and in our oceans – from chemicals like mercury that accumulate in fish to plastic waste that is strangling our oceans.

Vertebrates are disappearing fast

Earth’s entire vertebrate population has fallen 52 percent in the last 45 years, and the threat of extinction still looms for many including an estimated 41 percent of all amphibian species and 26 percent of mammals.

Humans are not safe either

With a global population of about 7.5 billion, humans may not be seen as in danger, but that could change very quickly. We are reliant on healthy ecosystems for food, water and other resources. Adjusting to mass extinctions would be a challenge under any circumstances, but it’s especially daunting in the context of climate change.

Read more: The Guardian

https://www.theguardian.com/environment/2017/jul/10/earths-sixth-mass-extinction-event-already-underway-scientists-warn

National Geographic:

https://news.nationalgeographic.com/2015/06/150623-sixth-extinction-kolbert-animals-conservation-science-world/

Alberton Record:

https://albertonrecord.co.za/189020/6th-mass-extinction-earth-happening-now-man-made/

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